WASHINGTON — With one justice declaring there are "two kinds of marriage: the full marriage, and then this sort of skim milk marriage," the U.S. Supreme Court on Wednesday seemed poised to strike down a federal law denying benefits to legally wed gay couples.

Questions from the court's four liberal justices and its swing vote, Justice Anthony Kennedy, sided with critics of the 1996 Defense of Marriage Act, which defines marriage as between a man and woman.

Kennedy appeared to reject the argument that the law was solely to provide uniformity. Because it applies to about 1,100 benefits and programs, he said, it makes government "intertwined with the citizens' day-to-day life" and runs the "real risk" of conflicting with states' rights to regulate marriage.

"It's not really uniformity because it regulates only one aspect of marriage. It doesn't regulate all of marriage," Kennedy told Paul Clement, lawyer for a U.S. House Republican group that stepped in to defend the law widely known as DOMA after President Barack Obama deemed it unconstitutional.

Hundreds of gay marriage supporters assembled outside were decidedly more upbeat than Tuesday, when the court was hesitant to go too fast in ruling on a California initiative that reversed gay marriage.

"It went beautifully," said Edith Windsor, the 83-year-old New York woman who brought the DOMA case after being denied an estate tax exemption for her deceased spouse.

Marveling in the sunshine, before a wall of reporters, Windsor spoke of how public attitudes have evolved. Ten years ago, she said, "I'd have been hiding in the closet."

New York, eight other states and the District of Columbia recognize gay marriage, while 12 others allow civil unions or domestic partnerships. If DOMA is ruled unconstitutional, gay couples would be eligible for a host of benefits, from tax breaks to survivor benefits.

As with Tuesday, the arguments began with a technical series of questions over legal standing — from the House Republicans' right to intervene to Obama's decision to join the case against the law while still enforcing it.

"I don't see why he doesn't have the courage of his convictions and execute not only the statute, but do it consistent with his view of the Constitution, rather than saying, oh, we'll wait till the Supreme Court tells us we have no choice," Chief Justice John Roberts vented.

But on the merits, there was a strong sense DOMA is in a precarious spot with a five-member majority of justices.

It was Justice Ruth Bader Ginsburg who made the milk analogy, suggesting the federal law created two types of marriage.

"With respect, Justice Ginsburg, that's not what the federal government is saying," Clement replied, saying it was assumed the government has authority to define terms that appear in statutes. He argued that the government has "a legitimate interest to weigh into the debate" and define marriage for the purpose of a variety of benefits and obligations.

Clement explained that at the time DOMA passed under President Bill Clinton, Hawaii was considering gay marriage and lawmakers were concerned that it would force acceptance by the federal government and other states. "And what Congress says is, wait a minute. Let's take a time out here. This is a redefinition of an age-old institution. Let's take a more cautious approach where every sovereign gets to do this for themselves."

But he was again put on the defensive by Justice Elena Kagan, who quoted a House report on DOMA that said, "Congress decided to reflect an honor of collective moral judgment and to express moral disapproval of homosexuality."

"Is that what happened in 1996?" Kagan pointedly asked Clement, causing a stir in the courtroom.

"Sure, the House report says some things that we are not — we've never invoked in trying to defend the statute," he replied. "But the House report says other things, like Congress was trying to promote democratic self-governance."

At one point, Donald Verrilli, the U.S. solicitor general, challenged that assertion.

"This statute is not called the Federal Uniform Marriage Benefits Act; it's called the Defense of Marriage Act. And the reason for that is because the statute is not directed at uniformity in the administration of federal benefits," he said.

Chief Justice Roberts asked Windsor's attorney, Roberta Kaplan, if she thought the 84 senators who voted for DOMA in 1996 were motivated by "bigotry."

Choosing her words carefully, Kaplan said many voted "based on an understanding that gay — an incorrect understanding that gay couples were fundamentally different than straight couples, an understanding that I don't think exists today."

Roberts also suggested the political shift in favor of gay marriage is due to interest-group lobbying. "As far as I can tell, political figures are falling over themselves to endorse your side of the case," he said.

Kaplan replied: "To flip the language of the House Report, Mr. Chief Justice, I think it comes from a moral understanding today that gay people are no different, and that gay married couples' relationships are not significantly different from the relationships of straight married people."

Windsor sued the government after she was denied a marriage exemption on $363,053 in estate taxes for her deceased spouse, Thea Spyer. She said it violated the equal protection component of the Fifth Amendment.

"If Thea was Theo," Windsor said Sunday on NPR, "I would not have had to pay" those taxes. "It's just a terrible injustice, and I don't expect that from my country. I think it's a mistake that has to get corrected."

DOMA was passed in the Clinton era when politicians almost universally objected to gay marriage. The former president now says he regrets signing the law.

In a March 7 op-ed column in the Washington Post, Clinton wrote that "it was a very different time. In no state in the union was same-sex marriage recognized, much less available as a legal right, but some were moving in that direction. Washington, as a result, was swirling with all manner of possible responses, some quite draconian." He went on to say that the thinking was DOMA would diffuse the effort to enact amendments banning gay marriage.

"When I signed the bill, I included a statement with the admonition that 'enactment of this legislation should not, despite the fierce and at times divisive rhetoric surrounding it, be understood to provide an excuse for discrimination,' " Clinton wrote. "Reading those words today, I know now that, even worse than providing an excuse for discrimination, the law is itself discriminatory. It should be overturned."

Clement urged the court to let the public decide. "That's what the democratic process requires. You have to persuade somebody you're right. You don't label them a bigot. You don't label them as motivated by animus. You persuade them you are right. That's going on across the country. . . . Allow the democratic process to continue."

The court is expected to rule on both same-sex marriage cases in late June.